In cold climates, dwellings are not only insulated but are substantially airtight to avoid heat loss. It is accordingly essential to provide for an adequate ventilation of the dwellings, and this is more and more accomplished by adjoining to the ventilation system, air-to-air heat exchangers to transfer the heat content of the expelled stale air to the incoming fresh and cold air, therefore maintaining the heating cost within reasonable limits. Known air-to-air heat exchangers for the purpose described are quite complex in their construction and, therefore, costly to manufacture and, moreover, they require special knowledge and tools to effect cleaning of the same. Therefore, the dwelling owner cannot generally effect maintenance of such heat exchangers. The above drawbacks are apparent, for example, in the Canadian Patent No. 1,153,360, issued Sept. 6, 1983 to Allen et al.